Measurements and Significant Figures IN THIS EXPERIMENT, YOU WILL Make measureme
ID: 1075379 • Letter: M
Question
Measurements and Significant Figures IN THIS EXPERIMENT, YOU WILL Make measurements using devices having different uncertainties Express measured quantities in a way that correctly shows the uncertainties of the measurements Use significant figures to properly represent measured and calculated quantities Investigate how to increase the number of significant figures in measured and calculated quantities by properly using measuring devices INTRO D UCTION Measurement is an important activity in most scientific studies. Every measurement contains an uncertainty that comes from the device or technique used to make the measurement. The numbers used to record a scientific measurement normally indicate the uncertainty in the measure- ment. For example, a mass recorded as 2.87 g indicates that the measurement has an uncertainty in the hundredths (.01) of a gram. This fact could be represented by recording the mass as 2.87 ± .01 g, but usually this is not done. The value is simply recognized as having an uncertainty of +1or-1 in the last recorded number. The numbers used to represent the certain part of a measurement (the 2 and 8 in the example), plus one number representing the uncertain part (the 7 in the example), are called significant figures or significant digits. Thus, the quantity 2.87 g contains three significant figures. The necessity of using zeros to express measurements raises the question of when zeros are considered to be significant figures. The measured mass expressed as 2.87 g could also be expressed as.00287 kg. The significance of a measurement cannot be changed simply by changing the units used to express the measurement. Thus, 00287 kg must contain three significant figures just as 2.87 g does. This is an example of one rule concerning zeros Zeros not preceded on the left by nonzeros do not count as significant figures Other zeros, those located between nonzeros and those to the right of nonzeros, are counted as significant figures. Thus, 3.509 g and 2.870 g both contain four significant figures, and both indicate that the measurement uncertainty is +.001 or-001 gExplanation / Answer
Procedure: Throughout this experiment, always use the most precise measuring tool possible to make your measurements. Remember that you can read the scale on the ruler and micrometer, then estimate one more digit to get the correct number of significant figures.
1. Record the zero reading of the micrometer in mm. This is the reading it has when it is closed. Only use the small knob at the end of the micrometer to close it!
2. Measure the diameter of the object at least six times in six different places along the length of the object. Alternate between you and your lab partner. Average the results of the measurements. Subtract the zero reading to get the corrected average diameter.
3. Record the zero reading of the Vernier calipers in cm.
4. Measure the length of the object at least six times using the most precise tool possible. Alternate between you and your lab partner. Average the results. If you used the Vernier caliper, subtract the zero reading from your average.
5. Zero the triple beam balance. Determine the mass of the object in grams (g) to the correct precision and record it
6. Convert all corrected average length and diameter measurements to cm. Use the mass you found in step 5 to calculate the density of the object in g/cm3 . Record your answer to the correct number of significant figures.
7. Compare your calculated density from step 6 with the actual density of the object. Look at the densities in the table in this lab. If there are any other properties that help you identify the substance it is made of (such as its color), take this into account. Calculate a percent error between your experimental value and the accepted value, and report it with the correct number of significant figures. If your error is greater than 7%, find the problem and correct it.
Do the above steps for both cylinders and record them on your answer sheet.